1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly to, an apparatus for controlling an operation of a reciprocating compressor, and a method therefor.
2. Description of the Background Art
In general, a reciprocating compressor sucks and compresses a refrigerant gas by linearly reciprocating a piston in a cylinder, and discharges the compressed refrigerant gas. The reciprocating compressor is classified into a recipro method compressor and a linear method compressor according to a method for driving a piston.
In the compressor using the recipro method, a rotary force of a rotary motor is transformed into a reciprocating motion by coupling a crank shaft to the rotary motor and coupling a piston to the crank shaft, but in the compressor using the linear method, a piston coupled to a mover of a linear motor performs a linear motion.
The linear method reciprocating compressor does not have a crank shaft for transforming a rotary motion into a linear motion, does not generate a friction loss by the crank shaft, and thus shows higher compression efficiency than a general compressor.
When the reciprocating compressor is used for a refrigerator or an air conditioner, a compression ratio of the reciprocating compressor can be changed by varying a voltage applied to a motor of the reciprocating compressor. It is thus possible to control a cooling capacity of the refrigerator or the air conditioner.
A conventional apparatus for controlling an operation of a reciprocating compressor and a method therefor will now be explained with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram illustrating the conventional apparatus for controlling the operation of the reciprocating compressor.
Referring to FIG. 1, the conventional apparatus for controlling the operation of the reciprocating compressor includes: a current detection unit 4 for detecting a current applied to a motor of the reciprocating compressor; a voltage detection unit 3 for detecting a voltage applied to the motor of the reciprocating compressor; a stroke estimator 5 for operating a stroke of the reciprocating compressor on the basis of the detected current value, the detected voltage value and parameters of the motor (for example, resistance of the motor, inductance of the motor and motor constant); a comparator 1 for comparing the operated stroke estimated value with a predetermined stroke reference value, and outputting a difference signal according to the comparison result; and a controller 2 for controlling the stroke of the reciprocating compressor by varying the voltage applied to the motor of the reciprocating compressor.
The operation of the conventional apparatus for controlling the operation of the reciprocating compressor will now be explained with reference to FIG. 2.
FIG. 2 is a flowchart showing sequential steps of the conventional method for controlling the operation of the reciprocating compressor.
As shown in FIG. 2, the conventional method for controlling the operation of the reciprocating compressor includes the steps of: detecting the voltage and current applied to the motor of the reciprocating compressor (S20); operating the stroke estimated value of the reciprocating compressor on the basis of the detected voltage value, the detected current value and the parameters of the motor (S21); comparing the operated stroke estimated value with the predetermined stroke reference value (S22); decreasing the voltage applied to the motor when the operated stroke estimated value is larger than the predetermined stroke reference value (S23); and increasing the voltage applied to the motor when the operated stroke estimated value is smaller than the predetermined stroke reference value (S24).
The conventional method for controlling the operation of the reciprocating compressor will now be described in more detail.
The voltage detection unit 3 detects the voltage applied to the motor of the reciprocating compressor and outputs the detected voltage value to the stroke estimator 5, and the current detection unit 4 detects the current applied to the motor of the reciprocating compressor and outputs the detected current value to the stroke estimator 5 (S20).
The stroke estimator 5 operates the stroke estimated value of the reciprocating compressor by applying the detected current value, the detected voltage value and the parameters of the motor to following formula 1, and outputs the operated stroke estimated value to the comparator 1 (S21).
                    x        =                              1            a                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                                                                  ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        〈                  Formula          ⁢                                          ⁢          1                〉            
Here, R represents the resistance of the motor, L represents the inductance of the motor, α represents the motor constant, VM represents the voltage value applied to the motor of the reciprocating compressor, and i represents the current value applied to the motor of the reciprocating compressor.
The comparator 1 compares the operated stroke estimated value with the predetermined stroke reference value, generates the difference signal according to the comparison result, and outputs the difference signal to the controller 2 (S22).
The controller 2 controls the stroke of the reciprocating compressor by varying the voltage applied to the motor of the reciprocating compressor on the basis of the difference signal. That is, when the operated stroke estimated value is larger than the predetermined stroke reference value, the controller 2 decreases the voltage applied to the motor of the reciprocating compressor (S23), and when the operated stroke estimated value is smaller than the predetermined stroke reference value, the controller 2 increases the voltage applied to the motor of the reciprocating compressor (S24).
Accordingly, the conventional method for controlling the operation of the reciprocating compressor controls the voltage applied to the motor of the reciprocating compressor by detecting the voltage and current applied to the motor of the reciprocating compressor, and operating the stroke estimated value of the reciprocating compressor in a sensorless method on the basis of the detected voltage and current.
However, in the conventional apparatus for controlling the operation of the reciprocating compressor and the method therefor, when the load on the motor of the reciprocating compressor is overloaded, a magnetic flux density generated in a coil of the motor is saturated, and thus the motor constant has non-linear characteristics. As a result, errors are generated due to the motor constant in the operation of the stroke estimated value of the reciprocating compressor, and thus the stroke of the reciprocating compressor is not normally controlled.